The easiest way to gain a little extra capacity from 194cc TLR 200 motors, is to
bore the cylinder to 67mm to accept the easily available pistons intended for Honda
industrial engines. This is especially useful for anyone who has an engine suffering
from cylinder wear, as oversize pistons for the TLR200 are not available from Honda,
and fitting higher compression pistons intended for other applications can cause
problems, as its not possible to adjust ignition timing to work properly with higher
compression ratios. The 67mm overbore results in a capacity of 203.78cc, over the
stock 194.76cc.

Fitting a 64.9mm stroke crank intended for TLR250 or RTL250 models, will in combination
with overbore to 67mm, provide a capacity of 228.81cc, but careful attention has
to be paid to clearance between the con-rod and gear box pinions, when the piston
is at BDC. Ideally to avoid problems here the close ratio gearbox from the TLR250
or RTL needs to be fitted at the same time as the longer stroke crank. Fitting a
64.9 stroke crank alone, will give a capacity of approximately 220cc, and this was
something that was offered on the old 1970s RS machines. However excess heat can
be a problem with any of these types of conversions, and a cylinder with larger fins
and or an oil cooler are very good moves.

Big fin cylinder for TLR Honda

Click to enlarge

Honda TLR 200 big bore

Big fin cylinder for TLR Honda

Click to enlarge

With a bigger cylinder liner fitted its possible to use a 70mm piston in TLR200 engines,
but additional heat would mean that this is not really feasible when standard small
fin cylinders are being retained, however modifications to crankcase mouth are also
required, and ideally changes to the internal engine oil passages that will allow
fitting of an oil cooler are also well worth while. But while theoretically it’s
certainly possible to convert a 194cc motor to 250cc, the cost of this is likely
to be considerable, and a properly modified 194cc unit will work almost as well in
most situations.

Capacity increases help to provide noticeable additional torque when applied to the
TLR200, but the possible gains will not be fully realised unless careful attention
has not also been given to carburetion, ignition, and exhaust systems, and these
changes alone if properly carried out, will mean a far more competitive machine than
standard, which certainly doesn’t require the amount of work and expense needed for
some of what we have outlined above.

Finally the above is intended to provide an outline of what is actually possible
to achieve with the TLR200 motors, but we are unable to assist with this type of
work, as the costs of doing such conversions properly, very often mean it would be
cheaper to sell your TLR200 and buy a TLR250, rather than doing any of what is denoted
above (other than a simple overbore to 67mm).

* Finally please remember that all of the above information is provided on the strict
proviso that any modifications or changes not carried out specifically by Classictrial,
are not guaranteed or warranteed in any way, and are entirely the responsibility
of the individual carrying them out, and that Classictrial are not responsible in
any circumstances for damage or injury that may occur as a result of poor workmanship
*